X-ray lithography system

ABSTRACT

An x-ray lithography system is disclosed in which x-rays are generated by directing a high energy laser beam against a metal target to form an x-ray emitting plasma. The x-rays from the plasma are then directed through a mask towards a resist covered wafer to cause a patterned exposure on the wafer resist coating. The mask, the portion of the target which the laser beam strikes and the portion of the water to be exposed are all within an evacuated chamber. The laser, prior to entering the chamber, is split into two separate beams, each of which are focused and directed through a window in the side of the chamber towards the same spot on the target. Apparatus, including an air bearing, seal and positioner, is provided to move the target at periodic intervals. Similar apparatus is provided to move the wafer from exposure section to exposure section. The laser beam system includes a face pumped laser beam amplifier and unidirectional beam expanders to allow the maximum energy to be transferred to the laser beam by the amplifier. A series of two or more laser pulses are provided in order to maximize the energy obtained from the laser amplifier. A magnet and a membrane shield are also provided to prevent high energy particles and dust contaminants from the plasma from effecting the lithography process. A materials handling device is provided for moving wafers, targets and masks and an alignment system operating within the evacuated chamber, positions of the wafer with respect to the mask prior to the exposure thereof.

This is a continuation of application Ser. No. 06/852,108, filed Apr.15, 1986, now abandoned.

This invention relates to an x-ray lithography system and moreparticularly, to such a system in which x-rays are generated by a laserbeam striking a target with sufficient power to create an x-ray emittingplasma.

Semiconductor chips have been made by a process called lithography formany years. Typically, an energy source provides ultraviolet lightthrough a mask which causes a pattern to appear on a resist coatedsilicon wafer. The light not blocked by the mask exposes the resist onthe wafer and either the exposed or unexposed resist can be etched away,leaving a pattern on the wafer which can be further processed by knowntechniques.

As the demands for denser and denser semiconductor chips occur, alimitation on the use of ultraviolet light has been found. Thislimitation is due, among other reasons, to the wavelength of the lightand the ability to make optical systems with sufficient resolution. Bothof these reasons result in a finite size of line, in the order of1.0-1.5 microns, which can be placed on the chip. It has been known forseveral years that to break the density barrier of ultraviolet lightphotolithography processing, a different energy source must be used. Onetype of energy source which has been widely suggested has been x-rays,which have a shorter wavelength than ultraviolet light and do notrequire sophisticated optical devices. X-ray lithography was firstsuggested by Smith, et al, in U.S. Pat. No. 3,743,842 entitled SoftX-Ray Lithographic Apparatus and Process. Later, Nagel, et al, in U.S.Pat. No. 4,184,078 suggested using a plasma emitting x-ray source togenerate the x-rays. Of particular significance herein is the embodimentof Nagel et al in which a laser was focused on a metal target and causedthe plasma to be created. Improvements to the basic Nagel technique havebeen made by the assignee hereof in U.S. patent application Ser. Nos.669,440, 669,441 and 669,442, which relate to improvements in the x-raygenerating source means.

In accordance with one aspect of this invention, there is provided anX-ray lithography system having means for generating a pair of highenergy laser beams, and a chamber, to be evacuated, having a pair ofhermetically sealed windows in the side walls thereof, a first openingat one end thereof and a second opening at the other end thereof. Thesystem further has means for directing and focusing the pair of laserbeams through the windows towards a focal point at the first opening,means for holding, positioning and moving a target so that the targetmoves at the focal point while a vacuum seal is formed around the firstopening and means for holding and moving a resist covered wafer and forforming a vacuum seal over the second opening while the wafer is heldand moved. Lastly, the system includes control means for controlling thegeneration of the laser beam, the evacuation of the chamber and themovement of the target holding, positioning and moving means and thewafer holding and moving means.

One preferred embodiment of the subject invention is hereafterdescribed, with specific reference being made to the following Figures,in which:

FIG. 1 shows a prospective view, partially in cut-away, of the x-raylithography system of the subject invention;

FIG. 2 shows a plan front view of the wafer processing and a portion ofthe x-ray source of the x-ray lithography system of the subjectinvention;

FIG. 3 shows a more detailed side view, partially in cross section, ofthe x-ray source of the system of the subject invention;

FIG. 4 shows a more detailed front view, partially in cross section, ofthe x-ray source of the subject invention;

FIGS. 5 and 5A show one type of interface between the x-ray emittingchamber and the wafer of the subject invention;

FIG. 6 shows a drawing useful in understanding the operation of thesubject matter shown in FIGS. 5 and 5A;

FIGS. 7 and 7A show an alternate embodiment of the interface between thex-ray generating chamber and the wafer;

FIG. 8 shows a diagram of the target and associated target movingmechanism used in generating the x-ray emitting plasma;

FIG. 9 shows a bottom view of the target moving mechanism used tointerface the target and the vacuum chamber of the subject invention;

FIG. 10 shows the laser system and path of the laser beam used ingenerating the x-ray emitting plasma;

FIG. 11 is a schematic diagram representing the laser system of thesubject invention;

FIG. 12 shows the shape and position in the amplifier glass slab of thelaser beam during various passes through the amplifier, as shown in FIG.11;

FIG. 13 shows a three dimensional view of the component placement of thelaser system shown in FIG. 11;

FIGS. 14A, 14B and 14C represent respectively the top, front and sideviews of the view shown in FIG. 13;

FIG. 15 is an overall block diagram of the electrical control system ofthe subject invention;

FIG. 16 shows the manner in which FIGS. 16A and 16B are placed together;

FIGS. 16A and 16B show a more detailed electrical system diagram of thesubject invention;

FIGS. 17A and 17B show a flow diagram of the initiation procedure priorto utilizing the subject invention in production;

FIG. 18 shows a flow diagram of the stand-by operation of the subjectinvention;

FIG. 19 shows a flow diagram of the manner in which data is loaded intothe computer of the subject invention;

FIG. 20 shows a flow diagram of the manner in which the target may beloaded into the machine of the subject invention; and

FIG. 21 shows the manner in which the masks may be loaded into themachine of the subject invention.

Referring now to FIG. 1, X-ray lithography (XRL) system 10 is shown.System 10 includes a laser system 12, a materials handling system 14, anx-ray generating system 16, a wafer handling system 18 and a controlsystem 20. Laser system 12 includes of a high powered and highrepetition rate laser oscillator and amplifying means, together with aplurality of filters, shutters and mirrors, to cause a pair of powerfullaser beams to be directed into the x-ray generating system 16. Thedetails of the laser system 12 are explained hereafter with respect toFIGS. 11-14.

The x-ray generating system 16 includes an evacuated chamber 22 intowhich is focused a pair of laser beams 24 and 24A from laser system 12.The beams 24 and 24A are directed to strike a target 26 interfaced withchamber 22, causing a plasma to result. As with any plasma, x-rays areemitted, which x-rays travel through the evacuated chamber 22, andthrough the x-ray transmissive parts of a mask positioned within thechamber, towards a silicon wafer on wafer handling system 18. The maskand a desired portion of the wafer are placed and maintained in properposition and alignment by the material handling system 14. Each of thesystems 12, 14, 16 and 18 are controlled by the control system 20.

Referring now to FIG. 1, the material handling system 14 is shown andincludes a robot 28 having an arm and platform mechanism 30. Robot 28controls its arm and platform 30 to pick-up and move a member 32, suchas a wafer, target or mask. A stack of members 32 to be moved may beloaded into XRL System 10 using an SMIF container 34, which is designedto maintain a purified air atmosphere therein to avoid contamination ofthe member 32 while being moved or loaded. XRL System 10 includes tworeceptacles to receive SMIF containers 34, one in the front, as seen inFIG. 1, and the other on the side (not seen).

Robot 28 may be controlled to remove the members 32 inserted into system10 using container 34 and to stack them in various positions 36. Fromthe positions 36, robot 28 may later move an individual member 32 intoproper position, which position is described in more detail hereafter.After a wafer is completely processed it may be returned to container 34and when container 34 is full, it may be removed from system 10 andtaken to the next processing station. Similarly, unused masks or usedtargets can be removed using robot 28.

Referring now to FIG. 2, a plan view from the front of XRL System 10 isshown with the external panels removed so that the wafer handling system18 and portions of the x-ray generating system 16 seen. In FIG. 2, lasersystem 12 rests on a granite slab 38. Slab 38, in turn, rests on aplatform 40 which, rests on a second granite slab 42. While not seen inFIG. 2, granite slab 42 is held by a support above the control system20.

Both granite slabs 38 and 42 are designed to have very flat and uniformtop surfaces. This is particularly necessary in the case of support 42to enable wafer handling system 18 to properly operate and position thewafer being processed in proper alignment. Further, each of the graniteslabs 38 and 42 are extremely heavy, and thus, prevent any vibrationsfrom affecting the proper operation of system 10.

Granite slab 38 has a pair of vertical holes 44 and 46 positionedthrough the interior thereof to allow the two laser beams 24 and 24Afrom laser system 12 to be directed towards the x-ray generating system16. Each of the two holes 46 are aligned with a mirror 48 and 50respectively. Each of the mirrors 48 and 50, in turn, reflect the laserbeams 24 and 24A towards focusing lenses 52 and 54 respectively, whichfocus the laser beams at a small point on the target 26 area. Thedetails of this structure will be explained hereafter with respect toFIG. 4.

After the laser beams 24 and 24A have been focused on target 26, theresulting plasma at target 26 generates x-rays 56 throughout chamber 22,some of which are directed towards wafer 58. A mask, positioned withinchamber 22 between the plasma and wafer 58, causes a pattern of x-raysto strike wafer 58. This pattern exposes the resist layer covering wafer58 so that wafer 58 can be further processed.

Wafer 58 is moved in discrete steps by wafer handling system 18. Waferhandling system 18 includes a chuck 60 which is moveable in the X, Y, Zand theta directions, so as to properly position wafer 58 at the desiredplace in alignment with the pattern of x-rays 56 from chamber 22. It isnecessary that wafer 58 be very precisely positioned within a few tenthsof a micron because the various steps used in processing wafer 56require alignment to that accuracy. The wafer handling system 18 may beany conventional wafer stepper device, such as the one used in theUltrastep 1000 Photolithography System described in more detail in thename of Martin E. Lee, U.S. Pat No. 4,444,492 and entitled "Apparatusfor Projecting a Series of Images onto Dies of a Semiconductor Wafer".

Referring now to FIGS. 3 and 4, X-ray generating system 16 is shown inmore detail. More specifically, FIG. 3 shows a side view, including theinterior details of chamber 22, and FIG. 4 shows a front view, includinginterior details of chamber 22. Laser beams 24 and 24A, applied fromlaser system 12 through openings 44 and 46, are deflected by mirrors 48and 50 to pass through focusing lenses 52 and 54. In FIG. 4, focusinglens 54 is shown in cut-away and consists of a plurality of focusinglenses 62 . . . 64. Laser beams 24 and 24A pass through focusing lens 52and focusing lens 54 and are reflected by respective mirrors 66 and 68,positioned on the outside of chamber 22, through windows 70 and 72,respectively, towards target 26. Focusing lenses 52 and 54 and mirrors66 and 68 are positioned such that when laser beams 24 and 24A arefocused by lenses 52 and 54 and reflected by mirrors 66 and 68, theyimpinges upon a single small spot 74, which may be on the order of 50 to100 microns in diameter, on target 26. Thus, the center-line distancefrom lenses 52 or 54, respectively, to spot 74 as reflected by mirrors66 or 68, respectively, is equal to the focal lengths of lenses 52 or54.

Chamber 22 is desirably an evacuated chamber having a pressure of lessthan a few Torr. The gas remaining within chamber 22 is preferably aninert gas, such as helium. In order to maintain the vacuum, as laserbeams 24 and 24A enter into chamber 22, windows 70 and 72 arehermetically sealed with the sides of chamber 22. Target 26 ispositioned at the top of chamber 22 to allow it to both be moved and toprovide a vacuum seal, as described hereafter with respect to FIGS. 8and 9. The bottom of chamber 22 is also hydrodynamically sealed andmoveable across wafer 38 as described in more detail with respect toFIGS. 5, 5A, 6, 7 and 7A.

As laser beams 24 and 24A are focused by lenses 52 and 54 and reflectedby mirrors 66 and 68 towards a focal point spot 74, the temperature oftarget 26 increases to greater than a million degrees centigrade. Target26 may be any conventional metal material, such as stainless steel, andwhen the laser beams 24 and 24A are focused at spot 74, a plasma iscreated which emits x-rays 56 throughout the entire evacuated innerportion of chamber 22. One manner in which the plasma is emitted isdescribed in more detail in U.S. patent application Ser. No. 669,441 inthe name of James Forsyth and assigned to the assignee hereof.

When the plasma is generated, two types of contaminants are emitted fromthe plasma, in addition to the x-rays. The contaminants are dustparticles, which result from the evaporating metal, and chargedparticles. A magnet 76 may be placed around the outside of container 22,as shown in FIG. 3, or alternately, within container 22, and is poled todeflect the charged particles away from the critical area where thelithography processing is occurring. The positioning of magnet 76 shouldbe out of the path of laser beams 24 and 24A and thus preferably will beoutside of container 22. Much of the dust particles will fall harmlesslyonto the structure supporting windows 70 and 72 out of the path of thex-rays 56 critical to the lithography process. The dust particles in thex-ray 56 path will be blocked by an x-ray transmissive membrane 77.Membrane 77 may be a silicon membrane, held by a conventional support,and means may also be provided to move, or remove, membrane 77 togetherwith its support, in order to remove the dust particles collectedthereon from the x-ray path.

In order to make XRL system 10 useful in production applications, it isdesirable that target 26 have a life exceeding 4 to 8 hours. Onetechnique for extending the life of the target has been previouslydescribed in James S. Forsyth U.S. patent application Ser. No. 669,440and assigned to the assignee hereof. In that Patent Application, targetsin the shape of either a cassette held strip of metal or a metal drumshaped object were shown as being placed wholly within the evacuatedportion of chamber 22. In XRL System 10, a plate, or disc shaped objectis utilized as target 26. Laser beams 24 and 24A may be focused atseparate and distinct points along a plurality of different tracks ofthe disc shaped target 26. Further, it may be desirable to increase theusage of the disc material by firing a plurality of different laserpulses into areas in which cavities have been predefined on target 26,such as been described in U.S. patent application Ser. No. 669,440.Alternatively, a plurality of laser pulses may be fired into the targetarea for each exposure.

Target 26 may be held by a vacuum chuck 78, which is designed to bemoved in both a circular and longitudinal direction over a plate 80,extending from the upper portion of chamber 22. The movement of chuck78, and the held target 26, is under the control of a stepper motor 82and a linear movement device 84. Linear movement device 84 may include arotating screw which moves stepper motor 82 from the left to right, asseen in FIG. 4. Stepper motor 82 has a shaft extending therefrom whichcan be rotated in response to commands from the control system 20 byprecise amounts, thereby causing chuck 78, and target 26 held thereby,to rotate around the various tracks of target 26. As soon as a completerotation has occurred for a particular track, linear movement device 84may be engaged to move stepper motor 82 so that a rotation aroundanother track occurs. After all of the tracks of target 26 are used,target 26 is replaced by a new metal plate.

The shaft from stepper motor 82 is coupled to a ferrofluidic coupler 86having a stationary portion and a rotating portion. The stationaryportion may have air pressure and air vacuum lines coupled to it, which,in turn, are coupled to the rotating portion of coupler 86. Air pressureand vacuum paths are then coupled through shaft 88 to control both abellows device 90, used to raise or lower chuck 78, and a plurality ofvacuum ports, used to hold target 26 in place, depending on whether airis applied or removed through the ferrofluidic coupler 86. When it isdesired to replace target 26, bellows device 90 is raised, therebyraising chuck 78 so that the arm and platform 30 of robot 28 can removethe spent target 26 and replace it with a new target.

In order for a sufficient intensity of x-rays to be generated, theplasma created should be in the partially evacuated chamber 22. Thus, atleast the surface of target 28 which the laser beams 24 and 24A strikemust be in the partial vacuum.

The structure by which chuck 78 forms a vacuum seal for maintaining thepartial vacuum in chamber 22 and also forms an air bearing for allowingmovement of target 28, as well as allows target 26 to be properlypositioned so that laser beams 24 and 24A can be focused at spot 74,will be described hereafter with respect to FIGS. 8 and 9.

The bottom of chamber 22 has an opening 92 therein into which a mask 94is to be positioned. Mask 94 may be any conventional x-ray mask, such asa silicon membrane having a pattern of a heavy metal, such as gold,deposited thereon. The pattern portion contained on mask 94 should be inalignment with the opening 92 at the bottom of chamber 22. The remainingportion of mask 94 is a support for the silicon membrane and a pluralityof inlet and outlet paths for vacuum and pressure to be connected tomaintain the seal, provide an air bearing and properly position the maskwith respect to wafer 58. The exact manner in which the seal, airbearing and positioning occurs will be described hereafter with respectto FIGS. 5, 5A, 6, 7 and 7A.

Positioned generally in the lower part of chamber 22 above mask 94, isthe wafer alignment mechanism 96. Alignment mechanism 96 may be similarin concept to the alignment mechanism used to position and align wafersin conventional photolithography techniques, such as those utilized inthe Ultrastep 1000 stepper described in the aforementioned U.S. Pat. No.4,444,492. However, specific differences exist between the alignmentmechanisms of x-ray lithography system 10 and the prior art, due, inpart, to the requirement that the alignment techniques utilizes marks onmask 94 and mask 94 must be within the evacuated portion of chamber 22.

The alignment mechanism is best seen in FIG. 3 and includes a pair ofoptical emitters and detector units 98 and 100. Light is provided fromand reflected light is provided back to each of emitter and detectorunits 98 and 100 through a pair of moveable chambers 102 and 104. Eachof the chambers 102 and 104 is shown in the closed position in FIG. 3,which occurs when wafer 58 is being moved by wafer handling system 18.Light beams 106 and 108, provided from mercury arc lamps in the emitterportion of emitter and detector units 98 and 100, travels throughchambers 102 and 104, which function as a microscope, and is reflectedby mirrors 110 and 112 towards wafer 58. As long as a predefined opticalalignment mark is not in the path of the light from beams 106 and 108,light is reflected back along the same path towards mirrors 110 and 112.A small hole in the mirrors 110 and 112, coupled by a fiber optic cableto the detector part of emitter and detector units 98 and 100, providesa path for the reflected light to be detected. Whenever the alignmentmarkers appearing on wafer 58 are moved into the path of light beams 106and 108, the light is scattered away from the original path and thescattered light is detected by units 98 and 100 to indicate that thewafer has moved to a certain aligned position.

As soon as wafer 58 is properly positioned by the emitter and detectorunits 98 and 100, electrical signals are provided to control system 20,which, in turn, causes wafer handling system 18 to stop moving wafer 58.At the same time, signals are provided to cause moveable chambers 102and 104 to move out of the path of the x-rays 56 from spot 74 throughopening 92. The two moveable chambers 102 and 104 are each coupled tochamber 22 by bellows connectors 114 and 116 which allow the partialvacuum within chamber 22 to be maintained regardless of the position ofchambers 102 and 104. The light beams 106 and 108 are applied throughhermetically sealed windows 118 and 120 at the ends of chambers 102 and104. When moveable chambers 102 and 104 are moved out of the path of thex-rays 56, the laser beams 24 and 24A can be provided and focused onspot 74 to cause the x-rays to be generated and be applied through theevacuated interior of chamber 22 towards mask 94 to cause a pattern ofx-rays to be provided to wafer 58. Thereafter, the bellows connectors114 and 116 are controlled to move chambers back to the position shownin FIG. 3 and wafer 58 is moved and aligned in the next position in themanner previously described.

Referring now to FIGS. 5, 5A, 6, 7 and 7A, the air bearing, seal andmask to wafer gap monitoring mechanism between the bottom of mask 94 andthe resist layered surface of wafer 58 will now be described. Oneembodiment of this structure is shown in FIGS. 5 and 5A and includes amask support ring 122 having a silicon membrane 124 attached to thebottom side thereof. The pattern 125 on mask 94 is fabricated on theportion of silicon membrane which extends over an opening 126 of supportring 122. As seen in FIG. 4 and described herein in more detail, supportring 122 may be inserted in the bottom of chamber 122 in alignment withcertain inlet and outlet paths through which gas may be pumped orevacuated.

The inlet and outlet paths from chamber 22 extend into mask support ring122 and include vacuum paths 128 and 130, which are the inner two pathsfrom the center of support ring 122, as seen in FIG. 5 and 5A, a heliumpressure path 132 and an air, or nitrogen, pressure path 134. There is asignificantly longer distance between paths 132 and 134 than betweenpaths 128 and 130 or 130 and 132. A vacuum pump may be attached to theexit side of paths 128 and 130 near the bottom of chamber 22 and heliummay be pumped through path 132 and air, or nitrogen, may be pumpedthrough path 134 from the inlets to those paths near the bottom ofchamber 22.

The bottom of mask support ring 122 and silicon membrane 124 have aplurality of rings 138, 140, 142 and 144 therein. Ring 138 is coupled topath 128 and ring 140 is coupled to path 130. Thus, any gas which is inthe area of rings 138 or 140 is evacuated through paths 128 and 130. Inthe same manner, ring 142 is coupled to path 132 and ring 144, which issubstantially wider than the other rings 136, 138 and 140, is coupled topath 134.

Three prealignment notches 146 are positioned on the side of masksupport ring 122 and, together with corresponding solenoids 147, areused to prealign mask support ring 122 within the area of the bottom ofchamber 22. This is done during the time robot 28, shown in FIG. 1A,moves a mask 94, which includes mask support ring 122 and siliconmembrane 124, from the stack of masks into the position shown in FIG. 4.Once mask 94 is positioned by the arms of solenoids 147 extending intonotches 146, mask 94 is held in position by a vacuum path 149.

Referring now to FIG. 6, the manner in which mask support ring 122 andsilicon membrane 124 function to provide the vacuum seal, air bearingand mask to wafer vertical gap positioner will now be described. First,however, it should be understood that the interior portion of chamber 22is at a relative pressure of, for example, less than a few Torr,whereas, the outside of chamber 22 is at normal atmospheric pressure ofapproximately 760 Torr. Further, the distance between the patternportion 125 of membrane 124 and the top of wafer 58 must be criticallycontrolled to be approximately 30 microns. In addition, wafer 58 must bereadily moveable with respect to mask support ring 122 and siliconmembrane 124 without disturbing the pressure within the evacuated innerportion of chamber 22.

By providing a vacuum pump connection to paths 128 and 130 and byconnecting path 128 into the interior of chamber 22 by path 136, the lowpressure vacuum within chamber 22 is maintained, as indicated by thelines 148 and 150 in FIG. 6. The use of two or more channels, such aspaths 128 and 130, allows the pressure within chamber 22 to bemaintained at a relatively low value, such as less than a few Torr. Sucha vacuum seal has been previously utilized in the Varian Microsealsystem wafer transport and handling mechanism to maintain a vacuumwithin an electron beam chamber. However, if one could utilize thisstructure to additionally maintain the distance between membrane 124 andthe top of wafer 58 at a precise value as well as allow relativemovement on both sides of the seal, additional other structure could beeliminated.

To obtain these added features, paths 132 and 134 are utilized. Heliumis applied through path 132 and air, or nitrogen, is applied throughpath 134. By adjusting the pressure of the helium and the air, ornitrogen, applied through paths 132 and 134, a high pressure can buildup at point 152, shown in FIG. 6. This high pressure at point 152, inconjunction with the relatively low evacuated pressure at otherportions, such as point 154 beneath membrane 124 in the critical areaswhere the exposure takes place, maintains the distance between membrane124 and the top of wafer 58 at a precise distance. This distance can bevaried by varying the pressure of the helium and air passing throughpaths 132 and 134. Further, the high pressure at point 152 acts as anair bearing, allowing friction free movement between membrane 124 andwafer 58. Despite such movement, the evacuation at openings 128 and 130still maintains the vacuum within chamber 22 and on both sides of themembrane 124. Further, the constant evacuated pressure on both sides ofmembrane 124 prevents warping of membrane 124 from occurring.

Referring now to FIGS. 7 and 7A, an alternate embodiment of the conceptdescribed with respect to FIGS. 5, 5A and 6 is shown. In this instance,ring 144 of FIG. 5 is replaced by a series of small holes 156 throughthe membrane 124. In addition, three gap sensors 158 are included tosense the gap distance between membrane 124 and wafer 58. Such gapsensors may be of the type utilized in the Ultrastep 1000photolithography system to seek identical back pressure for each sensorto achieve a parallel alignment between membrane 124 and wafer 58.

Referring now to FIGS. 8 and 9, the vacuum seal and air bearing betweenthe chuck 78 holding target 26 and plate 80 at the top of chamber 22 isshown. Target 26 is held firmly against the recessed center of chuck 78by a plurality of vacuum supports 160, each of which has an evacuationport 162 at the center thereof connected to a vacuum pump (not shown).

When it is desired that target 26 be moved by motor 82 and/or linearmovement device 84, the nonrecessed peripheral edge of chuck 78 is toglide over plate 80. An air bearing and seal, similar to that describedwith respect to FIG. 6, in the peripheral edge of chuck 78 prevents lossof the vacuum from within chamber 22 and allows friction free movementof chuck 78 with respect to plate 80. In this instance, however, only asingle vacuum path 164 and a single air path 166 are utilized. Each ofthe paths 164 and 166 are connected to rings 168 and 170 at the bottomof chuck 78. The air pressure into path 166 and the vacuum from path 164causes the air bearing and seal, described with respect to FIG. 6. Inpractice it may be desirable to utilize a plurality of vacuum paths 164and rings 168 and a plurality of pressure paths 166 and rings 170, suchas shown in FIG. 6, in order to obtain the vacuum and adjust thedistance in a more accurate fashion.

Referring now to FIGS. 10, 11, 12, 13 and 14A through 14C, the lasersystem 12 will now be described. FIG. 10 shows the manner in which asingle laser beam 24 is generated by laser system 12, subsequentlypassed through a beam splitter to form the dual beams 24 and 24A thatare passed through the two holes 44 and 46, reflected by the two mirrors48 and 50 through focusing lenses 52 and 54 and reflected by the twomirrors 58 and 60 into the chamber 22. The reason that two beams 24 and24A are utilized is that the power required of the laser to create theplasma is so great that handling the beam with conventional mirror andfocusing equipment would result in short component lifetimes, even withspecial dielectric coatings. By reducing the intensity in each of thetwo laser beams 24 and 24A applied into chamber 22 by approximately 50percent, conventional component materials may be used with a normaluseful life for those materials. This is particularly important becausesome of the component materials through which the laser beam passes canbecome very expensive to replace.

FIG. 11 shows schematically the manner in which the dual laser beams 24and 24A are generated and FIG. 12 shows the shape and position of thelaser beam 24 during each of its three passes through the laseramplifier. FIG. 13 shows a three dimensional representation of thepositioning of each of the major components to be described in FIG. 11and FIGS. 14A, 14B and 14C show respectively, the top, front and sideviews of the three dimensional structure shown in FIG. 13. Hereafter,the individual components will be described in detail with respect toFIG. 11, with reference to FIG. 12 on occasion. Numerical designationsof the components have been added to FIGS. 13 and 14A through 14C, butno specific description is given.

In FIG. 11, a conventional laser oscillator 172 provides a narrow laserbeam 24 through an aperture 174. The beam 24 is reflected by mirrors 176and 178 through a spatial filter 180, which increases the size of thebeam 24 by approximately two times. It should be noted that the majorcomponents described in FIG. 11 have been marked with numericaldesignations in FIGS. 13 and 14A, 14B and 14C. However, the minorcomponents, such as mirrors 176 and 178 and aperture 174, have beendeleted from FIGS. 13, 14A, 14B and 14C to increase the clarity of thoseFigures.

The laser beam 24 from spatial filter 180 is again reflected by mirrors182, 184 and 186 and provided through the laser beam amplifier 188.Amplifier 188 consists of a neodynium doped slab of glass, surrounded bya pair of flash lamp elements 192 and 194. The laser amplifier 188 issimilar to the type described in William S. Martin et al U.S. Pat. No.3,633,126 and entitled "Multiple Internal Reflection Face Pumped Laser".Generally, the beam 24 incident to the laser amplifier 188 picks up theenergy stored in the glass resulting from energizing the flashlamps 192and 194. Thus, the laser beam 24 at the output of laser amplifier 188 issignificantly more powerful than the laser beam 24 incident thereto.

Next, the laser beam 24 is reflected by mirrors 196 and 198 back throughlaser amplifier 188 along the same path as previously traveled. When thelaser beam 24 exits amplifier 188 on the second pass, it is shaped andpositioned as shown by beam A, in FIG. 12.

Next, the laser beam 24 is directed by mirrors 200, 202 and 204 to enterspatial filter 206, which magnifies the size of the beam 24 by a factorof approximately 1.6 in all directions. Thereafter, the laser beam 24 isreflected by mirrors 208 and 210 through a shutter assembly 212. Shutterassembly 212 consists of a linear polarizer 214, Pockels cell 216 and asecond linear polarizer 218, which is rotated 90 degrees with respect tothe first polarizer 214. Pockels cell 216 is controlled by signals fromthe control system 20 and, as is well known, changes the polarization ofthe beam incident thereto by 90 degrees when enabled. Thus, when thePockels cell 216 is enabled, beam 24 continues to pass through shutter212 and when Pockels cell 216 is not enabled laser beam 24 is blocked bypolarizer 218. It should be noted that shutter 212 operates the same inboth directions, so that any reflected beam would be blocked just as thebeam originated within oscillator 172 is blocked when Pockels cell 216was not enabled. Thus, the enable signal for Pockels cell 216 fromcontrol system 20 should be a very short pulse, timed to only allow theprimary beam 24 pulse or pulses generated by oscillator 172 to pass, andto block any reflected beams.

Next, mirrors 220, 222 and 224 direct the laser beam 24 throughamplifier 188 a second time and mirrors 226 and 228 direct the thenamplified beam 24 back along the same path through amplifier 188. Uponexiting amplifier 188 for the second time, the laser beam 24 ispositioned and shaped as beam B shown in FIG. 12. It should be notedthat beam B is approximately 1.6 times as large as beam A due to themultiplication by spatial filter 206. Further, the mirrors 222 and 224direct the laser beam 24, during the second pass through amplifier 188,along a different path through glass slab 190 than occurred during thefirst pass.

The output from amplifier 188 is redirected by a prism 230 into ananamorphic beam expander 232. The anamorphic beam expander 232 consistsof three prisms, triangular shaped in one plane and rectangularly shapedin a second plane perpendicular to the first mentioned plane. Each ofthe three prisms act to expand the beam only in one direction. In thiscase, the three prisms 234, 236 and 238 of beam expander 232 expand thelaser beam only in the X direction.

Thereafter, the beam 24 from beam expander 232 is directed by a mirror240 through a spatial filter 242, which does not change the size of thebeam 24. Next, the beam 24 is directed by mirrors 244 and 246 through asecond shutter 248, which includes polarizers 250, Pockels cell 252 andpolarizer 254. Shutter 248 operates in the same manner as previouslydescribed with respect to shutter 212. In order to stop all reflectedbeams, it is desirable to use a pair of shutters within the system,since some light leaks through the shutters.

Next, the laser beam 24 is directed by mirrors 256, 258 and 260 througha second anamorphic beam expander 262, which includes prisms 264, 266and 268. Expander 262 again expands the beam 24 only in the X direction.From beam expander 262, the laser beam 24 is directed by mirrors 270 and272 through amplifier 188 for a third pass and mirrors 274 and 276redirect the beam 24 back through amplifier 188. During this third pass,the laser beam 24 appears as beam C in FIG. 12, which shows it has beengreatly expanded in the X direction, but remains generally the same sizein the Y direction as it was when it had the shape of beam B. Further,the mirrors position beam C at a different location along the slab 190so that the beam can pick up the energy in slab 190 in that position. Itshould be noted that the spatial filters 180, 206 and 242, anamorphicbeam expanders 232 and 262 and the cross sectional size of slab 190 areall selected so that laser beam 24 is expanded to not greater than the Ydimension size of slab 190 in the Y direction, but may be expanded tosignificantly greater than the Y dimension size in the X direction. Thistype of expansion allows laser beam 24 to absorb as much of the slab 190stored energy as possible.

Upon leaving amplifier 188, after the third pass therethrough, laserbeam 24 is directed by prism 278 through a third anamorphic beamexpander 280, consisting of prisms 282, 284 and 286, which expand beam24 in the Y direction so that it again becomes of generally circularcross section. From expander 280, the beam 24 is passed through isolator288 and directed by mirrors 290, 292 and 294 to a beam splitter 296.Beam splitter 296 splits the incident laser beam 24 into two separateand generally equal intensity beams 24 and 24A. One of the beams 24 frombeam splitter 296 is directed by mirrors 298 and 300 through opening 44to lens 52 and on to target 26, as previously described. The second beam24A from beam splitter 296 is directed by mirrors 302, 304 and 306through lens 54 towards target 26 utilizing opening 46 in the graniteslab 38.

The operation of laser system 12 is designed according to the followingconsiderations. The production of intense pulses the followingconsiderations. The production of intense pulses of soft x-rays by meansof focussing high peak power laser pulses onto suitable targets has animportant commercial application in the field of soft x-ray lithography.As described in the aforementioned U.S. Pat. No. 4,184,078, a pulsedneodymium laser is suitable for use in this application. When aneodymium laser is to be configured to generate a sufficiently intensepulse for such an application, one or more stages of amplification arenormally employed in conjunction with a pulsed, typically Q-switched,neodymium oscillator. The degree of amplification of such pulses whichcan be conveniently achieved in compact systems is typically limited bythe ability of optical surfaces employed subsequent to the amplifiersystem to withstand the intensity of the laser pulse without sufferingpermanent damage. This is especially true when multilayer dielectricoptical coatings are employed to improve the efficiency of laser beamtransport. By limiting the degree of amplification to that permitted bydamage considerations, the amplifier medium typically exhibitssignificant further amplification potential after the passage of thelaser pulse. This remaining amplification represents unused laser pumpenergy which is lost after a short interval of time due to radiativedecay of the excited laser state in neodymium. In other words, thisunused available energy corresponds to reduced system efficiency.

One approach to minimize this problem is to expand the cross sectionalarea of the laser beam immediately after amplification by the use oflenses and/or prisms. Such an approach is used in the NOVA system, alarge pulsed neodymium system installed at the Lawrence LivermoreNational Laboratory, Livermore, Calif., to enable the extraction of thehighest possible fraction of amplifier stored energy in the passage of asingle laser pulse. Such an approach creates a significant penalty inthe space devoted to housing the optical components of the laser system,that is, the output components are all substantially larger than theamplifier cross section. Typically, the cost to manufacturelaser-quality optical components increases more rapidly than their crosssectional area, so both space and component costs are rapidly increasedby this approach.

In the application of soft x-ray lithography, it is not necessary thatall of the x-rays required to expose a mask pattern onto a suitablephotoresist be delivered to the photoresist in a single pulse. Nagel, etal., have demonstrated multipulse x-ray lithography exposures using arepetitively pulsed Nd:YAG laser (Applied Optics 23, 1428 (1984). Thelaser system used in this work had a pulse repetition rate of 10 Hz, butrequired 20 minute exposure times into PBS photoresist as a result ofthe low intensity laser pulses used. Each laser pulse was separated intime by an interval which was long compared to the energy storage timein the amplifier. Thus, that system was not efficient.

In modern optical step-and repeat lithography machines, the timerequired to deliver ultraviolet light to achieve satisfactoryphotoresist exposures is typically in the order of a few hundredmilliseconds or so. Therefore, an x-ray step-and-repeat lithographymachine would be attractive for use in fine line production lithography,so long as the total exposure time is of the order of a few hundredmilliseconds or less. Thus, in the operation of the laser system 12, thesequence of laser pulses must be produced by oscillator 172 within atime window of less than a few hundred milliseconds for the purpose ofmaximum lithographic system efficiency.

Optimization of both x-ray production and laser system efficiencyrequires consideration of several factors. To insure that a highfraction of the energy obtained from a multistage, pulsed laseramplifier system will be focussable to a high intensity, one or morespatial filters are typically included in the laser system. A spatialfilter typically consists of a pair of positive lenses separated by thesum of their individual focal lengths, with a small pinhole located atthe common focus. (See, for example, Hunt, et al., Applied Optics 17,2053 (1978)). In high peak power systems designed for x-ray production,the laser intensity near the common focus will be so high as to causeair breakdown and a consequent loss of transmission through the filter.Thus, spatial filters in this application are typically evacuated.Nevertheless, some portion of the laser energy may strike the sides ofthe pinhole causing a plasma to form and expand into the pinhole. Suchplasma formation may render the pinhole opaque until sufficient timeelapses to allow the plasma to dissipate. This dissipation time limitsthe rate at which successive pulses may be propagated through the laseramplifier chain. If the hot material from the pinhole walls has anaverage velocity of 50,000 cm/sec (corresponding to approximately 1000degrees K), then a pinhole of typically 200 microns in diameter wouldrequire a minimum of from 200-400 nsec to clear. This sets a lower limiton the interpulse spacing.

This lower limit is consistent with the time required for the x-rayemitting plasma formed at the surface of the laser target to dissipateand thus to permit the unobstructed formation of a new, x-ray emittingplasma by a subsequent laser pulse. The formation of a hot plasma by afocussed laser pulse onto a solid surface is typically accompanied bythe production of a small crater in the solid material. Subsequent laserpulses focussed into such a crater show increased x-ray productionefficiency as described in U.S. Pat. application Ser. No. 669,440, filedNov. 11, 1984.

In a pulse-pumped, flashlamp driven laser system such as neodymium, theoverall optimum conversion of power supply electrical energy into storedlaser energy occurs when the flashlamp current pulse has approximatelythe same duration as the characteristic laser energy storage time of theamplifying medium. This sets an upper limit on the interpulse spacingfor best efficiency.

Referring now to FIGS. 15 and 16A and 16B, as connected as shown in FIG.16, the control system 20 of the subject invention will now bedescribed. The heart of control system 20 is a pair of centralprocessing units (CPU) 308 and 310. CPU 308 may be an HP 300minicomputer manufactured by Hewlett Packard of Palo Alto Calif. andgenerally is used to control the wafer handling system 18. CPU 310 maybe an 8088 type microprocessor manufactured by Zendex or equivalent andgenerally controls the remaining apparatus and timing within the system.CPU 308 is connected to a pair of buses 312 and 314. Bus 312interconnects CPU 308 with various portions of wafer handling system 18,such as the stepper motors 316, laser interferometer 318, gap adjustmechanisms 320 and stage motion mechanisms 322. Bus 314 connects CPU 308and CPU 310 so that they may communicate with each other. Further, aprinter 324, photo multiplier tube (PMT) 326 and alignment mechanisms328 are connected to bus 314.

CPU 310 is further connected to a bus 330 to which a plurality ofdifferent components receive commands from or provide information to CPU310. These include slab laser 332, utilities 334, oscillator 336, loader338, target 340, diagnostics 342, debris control 344, displays 346 andkeyboard 348.

Referring now to FIGS. 16A and 16B, a more detailed diagram of thecontrol system 20 of FIG. 15 is shown. It should be noted that FIGS. 16Aand 16B should be placed together in the manner shown in FIG. 16. InFIG. 16A, the busses 312 and 314 of FIG. 15 have been combined into asingle bus 314, from which bus 312 exits.

CPU 308 is coupled to bus 314 to provide various signals to both CPU 310and the various blocks to the left of bus 314. These blocks include thelaser interferometer 318, which provides wafer position and error signalback to bus 314. The alignment circuitry 328 is shown as an X motionalignment system 328A and a Y motion alignment system 328B, each ofwhich receives destination and tolerance signals and provides a currentposition signal. Finally, the PMT system responds to the set gain andset threshold signals applied thereto from CPU 308 over bus 314.

Bus 312 couples bus 314 to a 32 bit interface circuit 350, whichprovides timing signals to the gap adjust circuits, shown as tip tilt320C, cross mask 320A and object positioner 320B. In addition, timingsignals are provided to the stepper motors 316, the shutter 322A, andthe wafer load 322B, the latter two of which form a part of the stagemotion device, shown in FIG. 15.

CPU 310 responds to signals from CPU 308, as well as provides signalsthereto, over bus 314. In addition, CPU 310 provides a Ready For Shotsignal to oscillator 336 and responds to a Shot Complete signal fromoscillator 336. Oscillator 336 may be the electronics associated withlaser oscillator 172. In addition, CPU 310 provides the Load Mask andUnload Mask signals to Mask Load circuit 338 and responds to the MaskReady signal from circuit 338. Lastly, CPU 310 responds to the Go ToCassette and Go To Exp Pos signals from Mask Load circuit 338.

CPU 310 provides a System Initialized signal to each of the variouscircuits 336, 338, 332A, 344, 332B, 342, 334B, 334E, 340A, 340B, 340C,334A, 334D, 334B and 334C within system 20. Upon the occurrence of theSystem Initialized signal, each of the circuits is initialized toperform its intended function. The System Initialized signal is providedduring the Initialization of system 10 described hereafter with respectto FIG. 17A and 17B.

Oscillator 336 responds to the Ready For Shot signal from CPU 310 andvarious status signals, such as the Distilled Water Temperature statussignal from DI Water circuit 334A, the Helium status signal from Heliumcircuit 334D and the Target Status signal from Focus circuit 340B.Assuming all of the status signals are proper, Oscillator circuit 336,in response to the Ready For Shot signal, causes the laser pulse train,previously explained, to be provided and issues the Shot Complete signalto CPU 310. In addition, the Shot Complete signal is provided to theDebris Control circuit 334, the Target Position circuit 340C and theTarget Load circuit 340A. In order to control the provision of the laserpulse beams 24 and 24A, Oscillator circuit 336 responds to and providesa plurality of signals within the system. The signals provided by theOscillator circuit 336 include the Q-Switch On/Off signal, the InterlockRelay signal, the Start signal, the Set Q Switch voltage, the Set PFNvoltage, the Simmer Trigger signal, the Fire Q Switch Voltage signal,the

Trigger Lamps signal, the Trigger Pockels Cell signal and the StartAmplifier Charge signal. Oscillator 336 responds to the Main PowerInterlock signal, Door Interlock Signal, Thermal Interlock signal, theFlow Interlock signal, the Q-Switch Voltage Monitor signal, the SimmerMonitor signal, the Q Switch Monitor 1 and Q-Switch Monitor 2 signalsand the PFM Voltage Monitor signal.

Referring now to FIG. 16B, the slab amplifier circuit 332A responds tothe Glycol and Water Flow Status and Glycol and Water Temperature Statussignals, as well as the Vacuum System Status, DI Water Flow Status andDI Water Temperature Status signals and Pockels Cell Status signal fromPockels cell circuit 332B. The slab amp circuit 332A further responds toexternal signals, including the External Trigger signal and the ExternalController Voltage signal. Other information provided the slab ampcircuit 332A includes the AT Volt signal, the HV Down Confirmationsignal, the Lamp Misfire signal, and the Door Interlock signal. Slab amp332A provides control signals to turn on the flash lamps of amplifier188 shown in FIG. 11, including the Ramp Up and Ramp Down signals, theTrigger Inhibit signal and the Laser Energy Off signal. In addition, theHV On and HV Off signals are provided from slab amplifier circuit 332A.

Pockels cell circuit 332B responds to the System Initialized signal fromCPU 310 and provides the Pockels Cell Status signal to slab amplifiercircuit 332A, in response to the Trigger Pockels Cell signal providedthereto from oscillator circuit 336. In addition, Pockels cell circuit332B receives the Pockels Cell Voltage Down and Pockels Cell OK signalsfrom circuits associated with the Pockels Cells 216 and 252, shown inFIG. 11.

The Diagnostic circuit 342 responds to the System Initialized signal,the Laser Output Diode, X-ray Output Diode, Oscillator Output Diode, andTrigger PC signals and provides the Adjust Wave Plate signal.

The Vacuum Control circuit 334E responds to the Systems Initializedsignal and the Exposure Tank Pressure, Spatial Filter Pressure, PumpEnclosure Interlock and the Door Interlock signals and provides theVacuum System Status signal to Slab Amplifier circuit 332A. In addition,Vacuum Control circuit 334E provides the Valve Open/Closed signal andthe Pumps On/Off signals.

Target Load circuit 340A responds to the System Initialized signal andthe Shot Complete signal from Oscillator 336. In addition, Target Loadcircuit 340A responds to the Sense Target Presence signal, the SenseMagazine Down Loader signal, the Sense Magazine In Up Position signaland provides the Load New Target signal, Unload Used Target signal, LoadTarget Magazine signal and Unload Target Magazine signal.

Focus circuit 340B responds to the System Initialized signal fromcomputer 310 and the Target Ready Signal from Target Position Circuit340C. In addition, Focus circuit 340B responds to the Sense Z PositionTarget signal and provides the Sense Z Position Of Target signal and theTarget Status signal.

Target Position circuit 340C responds to the System Initiate signal andthe Shot Complete signal and provides the Increment X Position andIncrement Y Position signals to the target mechanisms.

DI Water circuit 334A responds to the System Initialized signal and theOscillator Temperature Sense Signal, Oscillator Flow Sensor signal, SlabAmplifier Temperature Sensor signal and Slab Amplifier Flow Sensorsignal. Distilled water control circuit 334A provides the DI WaterTemperature Status signals and DI Water Flow status signals previouslydescribed.

Helium Control circuit 334D responds to the System Initialized signaland the Sense Input Valve and the Sense Helium output pressure signals.Helium control circuit 334D provides the Helium System Status signal tooscillator 336 and the Open/Closed Input Valve signal and the HeliumPumping System On/Off signals to control the helium pressure.

Air Interlock control circuit 334C responds to the System Initializedsignal, the Mask Cassette Out signal and the Mask Cassette In signal,the Mask In Place signal and the Outer Door Closed/Open Status signal.Air Interlock control circuit 334C provides the Unload Stepper Output,Load Stepper Output, Unload Stepper Input and Load Stepper Input controlsignals. In addition, Air Interlock control circuit 334C provides theClosed/Open Interdoor, Closed/Open Outer Door, Pump Out Entry, InnerDoor Closed/Open and Pressurized Entry control signals.

Glycol and Water control circuit 334B responds to the Initialize Systemsignal from CPU 310 and the Leak Detect 1, the Leak Detect 2, a pair ofOscillator Flow Sense signals and a pair of Slab Amplifier Flow Sensesignals and provides the Glycol and Water Temperature Status and Glycoland Water Flow Status signals to slab amplifier control circuit 332A.

Debris Control circuit 344 responds to the System Initialized signal andthe Shot Complete signal as well as the Sense Debris Shield and PockelsCell Trigger signal to provide an Advanced Shield signal to move themembrane shield 77 over the target to stop the dust particle debris.

Mask Load Control circuit 338B responds to the System Initialized signaland the Unload Mask and Load Mask signals from CPU 310. In addition,Mask Load Control circuit 338B responds to the Cassette Down Place 1signal and the Sense Mask signal provided thereto from the mask movingmechanisms. Mask Load control circuit 338B provides the Go To Cassetteand Go To Exp. Position signals to CPU 310 and additionally provides theElectromagnet On/Off signal to Go To Mask Slot signal, the Give Mask ToChuck signal and the Get Mask From Chuck signal.

As can be appreciated when viewing FIGS. 16A and 16B together, thecontrol of the system is accomplished by computer 310 and the programtherein which provides certain signals at certain times to cause certainevents to happen. Other things, once initiated, occur automatically insequence based on each of the various control circuits communicatingwith one another or with certain transducers throughout system 10.

Examples of the program control caused by CPU 310 on the overall systemare shown in FIGS. 17A, 17B, 18, 19, 20 and 21. Referring now to FIG.17A and 17B, the Initialize Program will be described. This program isexecuted whenever power is initially applied to the system.

First, according to block 360, a determination is made as to whether allpower has been turned on. If the answer is no, then according to block362, an error message is printed indicating that power is not appliedand the program aborts. Assuming that at block 360 power was determinedto be on, then according to block 364, the position of the xy stage,which is the chuck 60 of wafer handling system 18, is digitized.

Next, according to block 366, all stepper motors are returned to thehome position and the determination is made, as indicated at block 368,whether there are any motor errors. If so, the error message is printedand the program aborts. Assuming no motor errors, then, according toblock 372, the laser safety interlocks are digitized and, according toblock 374, a determination is made whether the digitized laserinterlocks are correct. If not, then according to block 376, the printerprints an error message and recommended operator action. Next, accordingto block 378, a determination is made whether the operator has commandedabort. If so, then according to block 380, the abort action occurs. Ifat block 378 the operator had taken the recommended corrective action, areturn to block 372 occurs and the laser interlocks are redigitized and,as indicated at block 374, rechecked.

Once the interlocks are determined to be correct at block 374, thenaccording to block 382, distilled water is turned on and a message isprinted so indicating to the operator. Next, according to block 384, thedistilled water interrupt is enabled and according to block 386 thelaser nitrogen is turned on and the message is printed to notify theoperator of such action. Next, according to block 388, the lasernitrogen interrupt is enabled.

Next, according to block 390, the glycol cooling is turned on and amessage is sent so indicating to the operator. Then, according to block392, the glycol interrupt is enabled and according to block 394, allshutters are closed. Thereafter, as indicated at block 396, adetermination is made whether all shutters have been closed. If not,according to block 398, an error message is printed and an abort occurs.Assuming the shutters were determined to be closed at block 396, then,as indicated at block 400, the laser oscillator is turned on at one-halfpower and according to block 402 a message so indicating is sent to theoperator. Next, according to block 404, the slab amplifier is turned onat one-half power, and according to block 406, a message so indicatingis sent to the operator.

Next, according to block 408, the frog arm is exercised. The term "frogarm" is the name given to the material handling system 14 robot 28 andarm 30, shown in FIG. 1A. As previously mentioned, the arm 30 of robot28 moves the masks, target and wafers within system 10. Next, accordingto block 410, a determination is made whether there are any frog armerrors, and, if so, the error message is printed and an abort occurs.

Assuming that the frog arm is properly operating, as determined at block410, then according to block 414, the two SMIF port elevators areraised. The SMIF port is the port which container 34 shown in FIG. 1 isinserted and includes an elevator therein for moving the items presentin the port to a position to be loaded onto the frog arm. Continuing atblock 416 in FIG. 17B, next, a determination is made whether the SMIFelevators are in the up position. If not, according to block 418, anerror message is printed and according to block 420, the operator isprompted to continue or to abort. If at block 422 it is determined thatthe operator determined to abort, then block 424 indicates the abort. Ifat block 422 it were determined that the operator desired to continue,then according to block 426 the status of each of the SMIF ports isstored and then a continuation at block 428 occurs. At block 428 thetarget magazine status is checked and next at block 430 a determinationis made whether targets are present. If it is found at block 430 that notargets were present, then according to block 432 the operator isprompted to load targets into one SMIF port. Next, at block 434, adetermination is made whether the targets are ready for loading. If not,a return to the beginning of block 434 occurs until such time as it isdetermined that targets are ready for loading. Once targets are readyfor loading, then according to block 436, the frog arm loads the targetsfrom the SMIF port to the storage tray and a return to block 430 occurs.At this point it is determined that the targets are present.

Continuing with block 438, the mask magazine status is checked and, atblock 430, a determination is made whether masks are present. If nomasks are present, then according to block 442, the operator is promptedto load the masks in the SMIF port. In addition, the message will informthe operator how many masks are to be loaded and, then at block 444, adetermination is made whether the masks are ready for loading into thesystem. Until such time as they are, the procedure remains at block 444.Once the masks are ready for loading into the system, then according toblock 446, the frog arm is instructed to get the top most mask from theSMIF port. Next, according to block 448, the mask ID is read from thetray and, according to block 450, the frog arm stores the mask in thestorage tray and records the position with respect to the ID read. Next,according to block 452, a determination is made whether the last maskhas been stored. If not, a return to block 446 occurs and blocks 446,448, 450 and 452 are repeated until the last mask has been stored in thestorage tray and its position recorded in connection with the mask IDnumber. Once the last mask has been stored, then a return to block 440occurs.

Once it is determined at block 440 that the masks are present, then,according to block 452, the operator is sent a message that the systemhas been initialized and according to block 456 the main menu isdisplayed. The initialization program then continues at point A as themain operating program, which is shown in FIG. 18.

Referring now to FIG. 18, the main system operating flow diagram will bedescribed. This diagram is used in conjunction with the displayed mainmenu and has been labeled as program A for convenience herein.Generally, program A, or the system operating program, is continuallyrepeated until the operator makes a selection from the main menu, inwhich case a branch to one of the other programs B through L occurs.When that selected program has been executed, a return to program Aoccurs and the program waits for the next operator command.

First, according to block 458, the user interface is initiated andaccording to block 460 the screens are cleared. Then, according to block462, the user menu is displayed. Next, according to block 464, adetermination is made whether a function request has been enteredpursuant to the user menu. If not, all of the error conditions arechecked, according to block 466, and if an error has been reported, asdetermined at block 468, the error condition is printed and an abortoccurs. If no error had been reported at the determination made at block468, a return to block 464 occurs and a wait for a function request oran error report occurs.

Once a function request has been found at block 464 a continuation withblocks 472-492 (even numbers only) occurs. Each of the blocks 472-492(even numbers only) represents each of the various functions which canbe requested. Whenever one of the functions has been determined to befound at one of blocks 472-492 (even numbers only), then a branch to arespective program B through L occurs.

The following functions correspond to the following programs which canbe selected according to blocks 472-492 (even numbers only):

    ______________________________________                                        Block No.   Function         Program                                          ______________________________________                                        472         Load Machine Data                                                                              B                                                474         Load Target      C                                                476         Load Mask Into Machine                                                                         D                                                478         Load Mask        E                                                480         Process Wafer    F                                                482         Print Data       G                                                484         Change Data      H                                                486         Read Status      I                                                488         Change Status    J                                                490         Diagnostics      K -492 Exit Menu L                               ______________________________________                                    

Examples of programs B, C and D, representing respectively, the LoadMachine Data, Load Target and Load Masks Into Machine programs, arehereafter given in FIGS. 19, 20 and 21. Others of the programs can bedeveloped, along the lines shown in FIGS. 19, 20 and 21 and theaccompanying descriptions thereto, for the programs E-L.

Referring now to FIG. 19 the Load Machine Data program B is shown.First, according to block 494, the machine data is loaded from the fileon the disk associated with computer 310. Next, according to block 496,the machine variables are updated based on information determined duringthe error and status checks. Lastly, according to block 498, the currentmachine operating variables are displayed and printed for the operator'sbenefit. Then a return to program A shown in FIG. 18 occurs.

Referring now to FIG. 20, program C, relating to the loading of thetargets is shown. First, according to block 500, a determination is madewhether target storage space exists. If not, the message "Target StorageFull" is displayed and a return to the main program A occurs.

Assuming at block 500 that target storage space was determined to exist,then, next, according to block 504, a determination is made whetherthere are targets in the front SMIF port. If not, a determination ismade at block 506 whether there are targets in the side SMIF port. Ifboth determinations at blocks 504 and 506 were no, then, according toblock 508, the operator is prompted to load targets into one SMIF portand, according to block 510, a determination is made if the targets areready. If not, a continuation with block 510 results until such time asit is determined that the ready condition exists. At that point, a clearsignal is issued and a return to block 504 occurs. If at block 506, itwere determined that the targets were in the side SMIF port, thenaccording to block 512 the side SMIF port is defined as the input port.If at block 504, it were determined that the targets were in the frontSMIF port, then according to block 514, the front SMIF port is definedas the input port.

In either case, a continuation at block 516 occurs and the frog arm iscommanded to move in the Z, or vertical, direction to the SMIF plateheight. Next, at block 518, the frog arm is commanded to rotate to thedesignated input port defined at block 512 or 514. Then, at block 520,the frog arm is extended to reach the SMIF plate at the designated inputport and, at block 522, the frog arm lowers the elevator. Next, at block524, the frog arm is retracted and, at block 526, a determination ismade whether the elevator is down. If not, an error message is printed,as indicated at block 528, and abort occurs, as indicated at block 530.Assuming the determination was made at block 526 that the elevator wasdown, then according to block 532, the top most target is located. Next,according to block 534, the z distance required for the frog to move toservice this target is calculated and at block 536, the frog arm ismoved to that calculated height, minus a small clearance. Next,according to block 538, the frog arm is extended to the target tray andat block 540, the frog arm is moved up by the clearance amount.

Next, according to block 542, the vacuum is turned on for the frog armhold down, so that it can take the target and, at block 544, the frogarm is retracted to the center. Then, at block 546, the frog arm isrotated to the storage area and, at block 548, the frog arm is extendedto the storage tray. Then, at block 550, the vacuum chuck is turned offso that the target can be stored and, at block 552, the frog arm islowered to clear the target and, at block 554, the frog arm is retractedback to the center to be out of the way.

Next, at block 556, a determination is made whether there are any moretargets. If not, a message is displayed that the target load is completeand a return to the main program A occurs. If at block 556 it weredetermined that there were more targets to be loaded, then, at block560, a determination is made whether there is target space available. Ifnot, then according to block 562, the message "Target Storage Full" isdisplayed and a returned to the main program A occurs. If, at block 560,it were determined that there was additional storage space, then, atblock 564, the frog arm is rotated back to the input port and a returnto block 536 occurs and the same process beginning with block 536 isrepeated until such time as a return to the main program, after eitherblock 558 or block 562, results.

Referring now to FIG. 21, program D, relating to loading masks into themachine, is shown. Program D is identical to program C, with theexception that the operations occur with respect to masks instead oftargets and with the further exception of the addition of blocks 566,568, 570 and 572 between blocks 544 and 546. Block 566 indicates thatthe frog arm, which was retracted to the center at block 544, is rotatedto the bar code reader and, then, according to block 568, the frog armis extended to the bar code reader. Then, at block 570, the mask ID isread by the bar code reader and, at block 572, the ID is stored withrespect to the storage position. Then, the program as previouslydescribed continues at block 546, where the frog arm is rotated to thestorage area and the mask is stored.

What is claimed is:
 1. In an x-ray lithography system in which agenerated laser beam is to be directed to strike a target to cause anx-ray emitting plasma to be created and in which a resist covered waferis placed in the path of said emitted x-rays, the improvementcomprising:laser beam splitter means for splitting said generated laserbeam into at least first and second laser beams, each of which has lessenergy than said generated laser beam; and first and second laser beamdirecting means for directing said respective first and second beamsover two separate paths towards a common spot on said target, at whichspot said plasma is created.
 2. In an X-ray lithography system of typein which X-rays are provided through a chamber towards a resist coveredwafer, said wafer being moved from exposure position to exposureposition, there being fixed reference alignment marks within saidchamber and corresponding alignment marks on each exposure portion ofsaid wafer, the improvement of alignment means comprising:means fordirecting light into said chamber along a path intersecting saidreference alignment marks and said wafer, said path being within amoveable member; means, responsive to the reflection of said light fromsaid wafer surface back along a path within said moveable member, for aproviding a signal manifesting a determination that said wafer alignmentmarks are in alignment with said reference alignment marks; and meansfor moving said moveable member from a first position blocking the X-raypath to a second position away from said X-ray path in response to saiddetermination of alignment signal; wherein said chamber is evacuated andsaid means for moving includes bellows means coupling said moveablemember to said chamber and for maintaining the vacuum within saidchamber during movement of said moveable number.
 3. An X-ray lithographysystem comprising:target means and resist covered wafer means, theresist covered surface of said wafer means having a plurality ofsections thereon to be exposed by the application of X-rays provided atsaid target means; an evacuated chamber having a window sealed in theside walls thereof, a first opening at one end of said chamber and asecond opening at the other end of said chamber; means for generatingand focusing a laser beam through said window towards a focal point;means external to said chamber for holding and moving said target meansso that a target surface of said target means moves while containingsaid focal point aligned with said first opening, said target holdingand moving means further forming a vacuum seal around said first openingwhile holding and moving said target means; means external to saidchamber for holding and moving said resist covered wafer means so onesection at a time of said wafer means is aligned with said secondopening, said wafer holding and moving means further forming a vacuumseal between said resist covered surface of said wafer means around saidsecond opening while holding and moving said wafer means; and controlmeans for controlling the generation of said laser beam, the evacuationof said chamber and the movement of said target holding and moving meansand said wafer holding and moving means.
 4. The invention according toclaim 3 wherein said means for holding and moving said wafer meansincludes air bearing and vacuum sealing means.
 5. The inventionaccording to claim 4 wherein said means for holding and moving saidtarget means includes air bearing and vacuum sealing means.
 6. Theinvention according to claim 3 wherein said means for holding and movingsaid target means includes air bearing and vacuum sealing means.
 7. Theinvention according to claim 3:wherein said first opening is encompassedby a first flat surface; wherein said means for holding and moving saidtarget means includes a second flat surface, at least a portion of whichis aligned with said first flat surface; and wherein one of said firstor second flat surfaces includes a flow path therethrough attached topressure providing means for maintaining a separation between said firstand second flat surfaces.
 8. The invention according to claim 7 whereinone of said first or second flat surfaces includes a second flow paththerethrough attached to evacuation means, said second flow path beingpositioned from said maintained separation at a location between saidfirst flow path and said first opening.
 9. The invention according toclaim 8 wherein second flow path includes a ring recessed into said onesurface.
 10. The invention according to claim 9 wherein said recessedring surrounds said first opening.
 11. The invention according to claim9 wherein said recessed ring surrounds said first opening during themovement of said target means.
 12. The invention according to claim3:wherein said second opening is encompassed by a first flat surface;wherein said means for holding and moving said wafer means includes asecond flat surface, at least a portion of which is aligned with saidfirst flat surface; and wherein one of said first or second flatsurfaces includes a flow path therethrough attached to pressureproviding means for maintaining a separation between said first andsecond flat surfaces.
 13. The invention according to claim 12 whereinone of said first or second flat surfaces includes a second flow paththerethrough attached to evacuation means, said second flow path beingpositioned from said maintained separation at a location between saidfirst flow path and said first opening.
 14. The invention according toclaim 13 wherein second flow path includes a ring recessed into said onesurface.
 15. The invention according to claim 14 wherein said recessedring surrounds said first opening.
 16. The invention according to claim14 wherein said recessed ring surrounds said first opening during themovement of said wafer means.
 17. The invention according to claim13:wherein said first opening is encompassed by a first flat surface;wherein said means for holding and moving said target means includes asecond flat surface, at least a portion of which is aligned with saidfirst flat surface; and wherein one of said first or second flatsurfaces includes a flow path therethrough attached to pressureproviding means for maintaining a separation between said first andsecond flat surfaces.
 18. The invention according to claim 17 whereinone of said first or second flat surfaces includes a second flow paththerethrough attached to evacuation means, said second flow path beingpositioned from said maintained separation at a location between saidfirst flow path and said first opening.
 19. The invention according toclaim 18 wherein second flow path includes a ring recessed into said onesurface.
 20. The invention according to claim 19 wherein said recessedring surrounds said first opening.
 21. The invention according to claim19 wherein said recessed ring surrounds said first opening during themovement of said target means.
 22. A method of fabrication semiconductordevices using X-rays generated in the interior of an evacuated chamberby focusing a laser beam pulses on a held target with sufficient powerto form an X-ray emitting plasma, said emitted X-rays exposing a patternon a held resist covered semiconductor substrate, said chamber includingfirst and second openings, said method comprising the steps of:movingsaid target means and forming a vacuum seal with said target meansaround said first opening as a target surface of said target means movesover said first opening while containing the focal point of said focusedlaser beam; and moving said substrate and forming a vacuum seal withsaid substrate around said second opening as said substrate moves fromone exposure position to the next adjacent exposure position.
 23. Themethod according to claim 22 wherein said step of moving said targetincludes:generating a high pressure zone between said chamber and meansfor holding said target; and evacuating a region between said zone andsaid evacuated chamber interior.
 24. The method according to claim 22wherein said step of moving said target includes forming an air bearingand seal between said chamber and the means for holding said target. 25.The method according to claim 22 wherein said step of moving saidsubstrate includes:generating a high pressure zone between said chamberand means for holding said substrate; and evacuating a region betweensaid zone and said evacuated chamber interior.
 26. The method accordingto claim 22 wherein said step of moving said substrate includes formingan air bearing and seal between said chamber and the means for holdingsaid substrate.
 27. A laser system comprising:a laser amplifier systemfor receiving and storing optical energy, said optical energy beingstored by said amplifier system for only a given time interval; aQ-switched laser oscillator for supplying a plurality of separate laserpulses within said given time interval to said laser amplifier system; alaser target system for multi-pulse X-ray production, including ametallic material capable of withstanding multiple, high intensity laserpulses; and means for directing the separate amplified laser pulses fromsaid amplifier system towards said laser target system.
 28. Theinvention according to claim 27 wherein said laser amplifier includes aglass slab and light providing means for directing light into said glassprior to said separate laser pulses passing therethrough.
 29. Theinvention according to claim 27 wherein said laser amplifier includes aglass slab and at least one flashlamp for directing said optical energyinto said slab for storage therein, a portion of said energy beingabsorbed by said separate laser pulses being directed through said slab.30. The invention according to claim 29:wherein at least one of saidmeans for directing includes a spatial filter; and wherein the timebetween each separated laser pulse provided by said oscillator isgreater than the time for any plasma formed within said spatial filterto dissipate.
 31. The invention according to claim 30 wherein said meansfor directing said laser pulses through said amplifier system directseach of said laser pulses through said amplifier system a plurality oftimes.
 32. The invention according to claim 31 wherein said means fordirecting said laser pulses from said amplifier system towards saidtarget system directs each of said plurality of laser pulses to the samespot of said metallic material.
 33. The invention according to claim27:wherein at least one of said means for directing includes a spatialfilter; and wherein the time between each separated laser pulse providedby said oscillator is greater than the time for any plasma formed withinsaid spatial filter to dissipate.
 34. The invention according to claim33 wherein said target system metallic material remains stationaryduring said plurality of laser pulses.
 35. The invention according toclaim 34 wherein said means for directing said laser pulses through saidamplifier system directs each of said laser pulses through saidamplifier system a plurality of times.
 36. The invention according toclaim 33 wherein said means for directing said laser pulses through saidamplifier system directs each of said laser pulses through saidamplifier system a plurality of times.
 37. The invention according toclaim 27 wherein said means for directing said laser pulses through saidamplifier system directs each of said laser pulses through saidamplifier system a plurality of times.
 38. The invention according toclaim 27 wherein said means for directing said laser pulses from saidamplifier system towards said target system directs each of saidplurality of laser pulses to the same spot of said metallic material.39. An X-ray lithography system comprising:a resist covered substrate; amask having a pattern thereon; a target aligned with said mask andsubstrate; and laser beam pulse producing means, including oscillatormeans and amplifier means, for providing a plurality of amplified laserbeam pluses to said target with sufficient power to cause an X-rayemitting plasma to be created, said X-rays being provided through saidmask to cause a pattern of X-rays to expose said resist coveredsubstrate; said amplifier means including a glass slab and a flashlampfor providing optical energy to said slab for storage by said slab foronly a given time period; and said oscillator means generating aplurality of unamplified laser beam pulses within said given time periodwherein said plurality of unamplified laser beam pulses are received bysaid amplifier means during said given time period.
 40. The inventionaccording to claim 39 wherein said laser beam pulse producing meansfurther includes spatial filters through which each laser beam pulsetravels and causes a plasma to be created, which plasma lasts for acertain time period, less than said given time period, each of saidplurality of unamplified laser pulses being separated by at least saidcertain time period.
 41. The invention according to claim 40 whereinsaid laser beam pulse producing means includes laser beam pulsedirecting means for directing each of said unamplified laser beam pulsesthrough said amplifier a plurality of times during said given timeperiod to obtain said amplified laser beam pulse.
 42. The inventionaccording to claim 39 wherein said laser beam pulse producing meansincludes laser beam pulse directing means for directing each of saidunamplified laser beam pulses through said amplifier a plurality oftimes during said given time period to obtain said amplified lase beampulse.
 43. The invention according to claim 39 wherein each of saidlaser beam pulses are directed to the same point on said target.
 44. Theinvention according to claim 39 wherein said laser oscillator is a Qswitched laser oscillator.
 45. The invention according to claim 39wherein said glass slab has two parallel faces into which said opticalenergy from said flashlamps is directed and end faces positioned at anangle to said parallel faces, said unamplified laser beam pulses beingdirected into one of said end faces and said amplified laser beam pulsesbeing provided from the other one of said end faces.
 46. The inventionaccording to claim 39 wherein each of said plurality of unamplifiedlaser beam pulses are separated from the next occurring one of saidlaser beam pulses by at least 100 nanoseconds.
 47. A method of providingamplified laser energy to an X-ray target so as to produce X-Rays saidlaser energy being amplified by a laser amplifier of a type whichreceives optical energy and stores said received optical energy for onlya given time interval, said method comprising the steps of:directingoptical energy towards said amplifier to energize said amplifier;generating a first laser beam pulse; providing said first laser beampulse through said amplifier to produce a first amplified laser beampulse; generating a second laser beam pulse and supplying said secondlaser beam pulse to said laser amplifier within said given time intervalafter the end of said step of directing; providing said second laserbeam pulse through said amplifier to produce a second amplified laserbeam pulse; and directing said first and second amplified laser pulsesfrom said amplifier to said object.
 48. The invention according to claim47 wherein said object is a target of a type from which an X-rayemitting plasma may be created, said method further comprising the stepof directing sufficient optical energy to said amplifier so that each ofsaid first and second laser beam pulses have sufficient power to createan X-ray emitting plasma upon being directed to said target.
 49. Themethod according to claim 48wherein said step of providing said firstlaser beam pulse includes providing said first laser beam through aspatial filter, so as to create a plasma in said first spatial filterduring a certain time interval, said certain time interval being lessthan said given time interval; and wherein said step of generating saidsecond laser beam pulse occurs after said certain time interval.
 50. Themethod according to claim 47wherein said step of providing said firstlaser beam pulse includes providing said first laser beam pulse througha spatial filter, so as to create a plasma in said first spatial filterduring a certain time interval, said certain time interval being lessthan said given time interval; and wherein said step of generating saidsecond laser beam occurs after said certain time interval.
 51. Themethod according to claim 47wherein said object is a target; and whereinsaid step of directing includesdirecting said laser beam pulses towardssaid target, creating and X-ray emitting plasma at the point said laserbeam pulses intersect said target, placing an patterned X-ray mask inthe path of said X-rays, and exposing a resist covered substrate with apattern of X-rays defined by said mask.
 52. The method according toclaim 51wherein said step of providing said first laser beam pulseincludes providing said first laser beam pulse through a spatial filter,so as to create a plasma in said first spatial filter during a certaintime interval, said certain time interval being less than said giventime interval; and wherein said step of generating said second laserbeam pulse occurs after said certain time interval.
 53. The methodaccording to claim 52 wherein said object is a target of a type fromwhich an X-ray emitting plasma may be created, said method furthercomprising the step of directing sufficient optical energy to saidamplifier so that each of said first and second laser beam pulses havesufficient power to create an X-ray emitting plasma upon being directedto said target.